Microwave drying characteristics of microalgae (<Emphasis Type="Italic">Chlorella vulgaris</Emphasis>) for biofuel production

Algal biofuels serve as a promising alternative energy source for liquid fuels. However, one of the bottlenecks in the conversion of microalgae to biofuels is the drying process. A moisture content of at most 10 % is desired for algal biomass prior to oil extraction to maximise biofuel yield. Conventional means of drying results to longer drying time and uneven drying of algal biomass. This study investigated the drying characteristics of microwave for microalgae (Chlorella vulgaris). Three microwave intensity levels (300, 600, and 900 W) were considered to dry 10, 20, and 30 of algal mass. Page model gave a better fit on the moisture ratio with time of microwave drying than the exponential model. Furthermore, the specific energy requirement was computed, and a relationship was found between moisture ratio with power and mass. Fourier transform infrared spectroscopy results showed significant reduction of infrared signal intensities of the functional groups present in the algae after drying at higher microwave power level. It was concluded that the 20 W/g microwave drying setting gave a lower specific energy requirement with good quality of remaining high lipid content qualitatively. Furthermore, it was recommended to use gas chromatography mass spectroscopy to further quantify the algal lipids and other functional groups.     

The Activation Energy <Emphasis Type="Italic">U</Emphasis>(<Emphasis Type="Italic">T</Emphasis>,<Emphasis Type="Italic">H</Emphasis>) in Y-based Superconductors

Based on the Arrhenius equation, a method to calculate the activation energy from the resistance transition is proposed for high temperature superconductors. This method is applied to the Y-based superconductors. The activation energy is found to be U(T,H)∼(1−T/T _c )^4.8(H/H ₀)^−3.8 of YBCO crystal, and U(T,H)∼(1−T/T _c )^3.3(H/H ₀)^−2.2 of Er doped MTG YBCO crystal, respectively. With the obtained activation energy U(T,H), the lower part of the experimental curve ρ(T,H) and its derivative can be reproduced.      

Long-wavelength photodiodes based on <Emphasis Type="Italic">n</Emphasis>-GaSb/<Emphasis Type="Italic">n</Emphasis>-GaInAsSb/<Emphasis Type="Italic">p</Emphasis>-AlGaAsSb heterostructures

Photodiodes sensitive in the wavelength ranges 1–2.5 μm and 1–4.8 μm at room temperature have been created on the basis of n-GaSb/n-GaInAsSb/p-AlGaAsSb double-junction heterostructures of two types. The broadband photosensitivity of the diode structures of both types is indicative of the complete separation of photogenerated electron-hole pairs in the staggered n-p heterojunction (n-GaInAsSb/p-AlGaAsSb). The noise characteristics of photodetectors based on the proposed diode structures have been studied. Prospects of the use of these devices in thermophotovoltaic cells for low-temperature radiation sources are considered.     

Impact-ionization-stimulated electroluminescence in isotype <Emphasis Type="Italic">n</Emphasis>-GaSb/<Emphasis Type="Italic">n</Emphasis>-AlGaAsSb/<Emphasis Type="Italic">n</Emphasis>-GaInAsSb heterostructures

We have studied electroluminescence in n-GaSb/n-AlGaAsSb/n-GaInAsSb heterostructures with isotype heterojunctions, in which the quantum efficiency of emission is increased due to the additional production of electron-hole pairs as a result of the impact ionization that takes place near the heterointerface. The impact ionization in such heterostructures is possible due to the presence of deep wells in the energy band structure.     

Speed of sound in <Emphasis Type="Italic">n</Emphasis>-hexane, <Emphasis Type="Italic">n</Emphasis>-octane, <Emphasis Type="Italic">n</Emphasis>-decane,and <Emphasis Type="Italic">n</Emphasis>-hexadecane in the liquid state

This paper describes an improved experimental facility for measuring the speed of sound in liquids with an accuracy of up to 0.1%. Measurements of the speed of sound in liquid n-hexane, n-octane, n-decane, and n-hexadecane at temperatures of 298–433 K and pressures of 0.1–100 MPa have been made. It has been shown that in the possible comparison range the obtained values of the speed of sound are in good agreement with the literature data. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 4, pp. 732–736, July–August, 2008.     

Synthesis,growth, optical,mechanical and electrical properties of <Emphasis Type="Italic">L</Emphasis>-lysine <Emphasis Type="Italic">L</Emphasis>-lysinium dichloride nitrate (<Emphasis Type="Italic">L</Emphasis>-LLDN) single crystal

Semi-organic nonlinear optical material, L-lysine L-lysinium dichloride nitrate (2C₆H₁₅N₂O₂⁺_{2}^{+} · H⁺ · NO₃^-_{3}^{-} · 2Cl⁻) was synthesized at room temperature. Single crystals of L-LLDN were grown by slow cooling solution growth technique. The grown crystal was confirmed by powder X-ray diffraction analysis. The crystalline perfection of the grown single crystal was characterized by high-resolution X-ray diffraction (HRXRD) studies. The cut-off wavelength was determined by UV-vis transmission spectral analysis. The frequency doubling of the grown crystal was confirmed by powder second harmonic generation (SHG) measurement. The refractive index and birefringence of the crystal were determined using He–Ne laser source. Mechanical property of the crystal was determined by Vickers hardness tester. The frequency and temperature dependence of dielectric constant (ε _r), dielectric loss (tan δ) and a.c. conductivity (σ _ac) were also measured.     

Project of laser-pumped quantum <Emphasis Type="Italic">M</Emphasis><Subscript><Emphasis Type="Italic">X</Emphasis></Subscript> magnetometer

The possibility of creating a new scheme of a laser-pumped quantum magnetometric device based on a double-beam M _X magnetometer is considered. The proposed system ensures the simultaneous measurement of the modulus of the Earth’s magnetic field vector (with an absolute accuracy of 0.02 nT) and two angles of deviation of this vector with an absolute accuracy and sensitivity of not worse than 0.4″ (0.1 nT) at a measurement time of τ = 1 s. In contrast to the known analogous systems, the proposed scheme does not require generating additional magnetic fields.     

Thermodynamic modeling of BC<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>N<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> chemical vapor deposition from mixtures of <Emphasis Type="Italic">N</Emphasis>-trimethylborazine and nitrogen

Thermodynamic modeling of the chemical vapor deposition of boron-carbonitride-based films in the B-C-N-H-O system using mixtures of N-trimethylborazine and nitrogen is carried out for reduced pressures (13.3 and 1.33 Pa) and a wide temperature range (300–1300 K). The source of oxygen impurities in this system is a residual pressure of 0.40 Pa. The results indicate that films of various compositions can be grown. The conditions for the deposition of BC _x N _y films are identified.     

The search for novel superhard and incompressible materials on the basis of higher borides of <Emphasis Type="Italic">s</Emphasis>, <Emphasis Type="Italic">p</Emphasis>, <Emphasis Type="Italic">d</Emphasis> metals

The state of the art in the search for novel superhard and (or) incompressible materials on the basis of higher borides of s, p, d metals has been briefly reviewed. The information has been considered about experimental and theoretical studies of the following groups of borides: diborides of 4d, 5d heavy metals (Tc, Ru, Rh, Re, Os, and Ir), hexagonal tetraborides with the WB₄-type structure, and AMB₁₄ borides (where A, M are s, p metals) as well as of a number of related systems.     

Nernst Signal in High-<Emphasis Type="Italic">T</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> Superconductors

The time-dependent Ginzburg–Landau equation with thermal noise is used to calculate the Nernst signal e _N , describing the Nernst effect, in type-II superconductor in the vortex-liquid regime. The Gaussian method used is an elaboration of the Hartree–Fock method. An additional assumption often made in analytical calculations that only the lowest Landau level significantly contributes to physical quantities of interest in the high-field limit is lifted by including all the Landau levels. The values of e _N are in good quantitative agreement with experimental data for temperature close to T _c on Bi₂Sr₂CaCu₂O_8+δ and Bi₂Sr₂Ca₂Cu₃O_10+δ .     

The Boundary Effect on the Energy Gap of High <Emphasis Type="Italic">T</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> Superconductors

Spatial dependence of the pairing potential across the thickness of the superconducting CuO₂ planes in high T _c superconductors (HTSC) copper oxides is found by using the Ginzburg-Landau-Gor’kov (GLG) theory. The potential turned out to be significantly suppressed due to an effect of non-superconducting layers, which separate the CuO₂ planes. The effect leads also to the reduction of the critical temperature of these superconductors. The temperature dependence of the effective energy gap was calculated in this work.     

Docosahexaenoic acid production from crude glycerol by <Emphasis Type="Italic">Schizochytrium limacinum</Emphasis> SR21

In our search for a substitute energy source, microalgal biodiesel has presented itself as a potential candidate. However, the development of biodiesel results in the overproduction of crude glycerol, which can cause undesirable environmental issues. The environmental harm can be minimized by converting crude glycerol into value-added products. One solution involves using a microalga Schizochytrium limacinum SR21 to convert crude glycerol into docosahexaenoic acid (DHA). DHA is an essential fatty acid, necessary for developing brain functions in infants and maintaining healthy brain activity in adults. In our study, the highest DHA productivity of 233.73 mg/g biomass was obtained using 3 % crude glycerol in Medium 2 at 20 °C under mixo/heterotrophic cultivation.     

Effect of <Emphasis Type="Italic">Azospirillum brasilense</Emphasis> and <Emphasis Type="Italic">Burkholderia unamae</Emphasis> Bacteria on Maize Photosynthetic Activity Evaluated Using the Photoacoustic Technique

In this work, the photosynthetic process of maize plants (Zea mays), which were grown using seeds inoculated with plant growth promoting bacteria Azospirillum brasilense and Burkholderia unamae, was monitored. Photothermal and photobaric signals obtained by a time-resolved photoacoustic measurement configuration were used for measuring the oxygen evolution rate in situ. A frequency-resolved configuration of the method was utilized to determine the oxygen diffusion coefficient and the thermal diffusivity of the maize leaves. The latter parameters, which can be used as indicators of the photosynthetic activity of maize, are found to vary according to the plant–microbe interaction. Treatment with plant growth promoting bacteria induced a decrease in the oxygen diffusion coefficient of about 20 %.     

Material Effect and Steam Explosion at High Temperature (<Emphasis Type="Italic">T</Emphasis> > <Emphasis Type="Bold">2300</Emphasis> K)

In the frame of nuclear power plant safety, the interaction of molten corium (mixture of materials coming from a power plant) with water can generate dynamic loading of the surrounding structures. This phenomenon is called the steam explosion. Many experiments have been performed in the KROTOS facility with simulation materials (Al₂O₃) and prototypical materials (U,Zr)O₂, and different behaviors attributed to a ‘material effect’ have been observed. Alumina melts produced spontaneous energetic steam explosions, whereas explosions with corium melts (80% UO₂–20% ZrO₂) must be triggered and are less energetic. These differences may be partly attributed to the formation of meta-stable gamma alumina and the ability of liquid alumina to dissolve part of the water, acting like an internal trigger. These results mean that alumina is probably not an adequate simulation of the corium for steam explosion. Paper presented at the Seventh International Workshop on Subsecond Thermophysics, October 6–8, 2004, Orléans, France.     

Inference with progressively censored <Emphasis Type="Italic">k</Emphasis>-out-of-<Emphasis Type="Italic">n</Emphasis> system lifetime data

A system with n independent components which works if and only if a least k of its n components work is called a k-out-of-n system. For exponentially distributed component lifetimes, we obtain point and interval estimators for the scale parameter of the component lifetime distribution of a k-out-of-n system when the system failure time is observed only. In particular, we prove that the maximum likelihood estimator (MLE) of the scale parameter based on progressively Type-II censored system lifetimes is unique. Further, we propose a fixed-point iteration procedure to compute the MLE for k-out-of-n systems data. In addition, we illustrate that the Newton–Raphson method does not converge for any initial value. Finally, exact confidence intervals for the scale parameter are constructed based on progressively Type-II censored system lifetimes.     

Nonlinear <Emphasis Type="Italic">p</Emphasis>-ary Sequences

Low correlation p-ary sequences with p an odd prime are constructed. They are obtained as Gray images of codewords of a subcode of the generalized Kerdock codes over the ring _p². They can be shown to be nonlinear in some precise sense. The research of this author is partially supported by NUS-ARF research grant R-146-000-029-112 and DSTA research grant R-394-000-011-422.This research was done while this author was visiting Temasek Laboratories and Department of Mathematics, NUS. The author thanks them for their hospitality.Keywords:Galois rings, Gray map, Kerdock code, CDMA.     

Effect of a thin <Emphasis Type="Italic">a</Emphasis>-SiO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>: H film on plasmonic properties of gold nanoparticles

Data on the optical properties of a nanocomposite material constituted by gold nanoparticles covered with a thin film of amorphous hydrogenated silicon suboxide have been obtained for the first time. The thin film was deposited by gas-jet electron-beam plasma chemical-vapor deposition. As gold particles situated on the surface of quartz glass are covered with a thin a-SiO _x : H film, their plasmonic resonance peak is shifted to longer wavelengths. The calculations made in the study demonstrated a good agreement with the experiment.     

Electrical and photoelectric properties of electrodeposited <Emphasis Type="Italic">n</Emphasis>-Si/<Emphasis Type="Italic">n</Emphasis>-Cd<Subscript>1 - <Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript>x</Subscript>S heterojunctions

n-Si/n-Cd_{1 - x} Zn_xS heterojunctions are produced by electrodepositing Cd_{1 - x} Zn_xS (0 x 0.6) films on silicon substrates, and their electrical and photoelectric properties are studied. The results demonstrate that the spectral response of the heterojunctions depends strongly on the film composition and heat-treatment conditions. The highest photosensitivity is achieved at x = 0.6 by heat treatment at 350°C for 7 min: V _OC = 0.5 V and I _SC = 3.8 mA/cm² under illumination of 1500 lx at 300 K.Translated from Neorganicheskie Materialy, Vol. 41, No. 3, 2005, pp. 276–280.Original Russian Text Copyright © 2005 by Mamedov, Gasanov, Amirova.This revised version was published online in April 2005 with a corrected cover date.This revised version was published online in April 2005 with a corrected cover date.     

Investigation of mechanical and superconducting properties of iron diffusion-doped <Emphasis Type="Italic">Bi</Emphasis>-<Emphasis Type="Italic">2223</Emphasis> superconductors

The mechanical and superconducting properties of the Fe diffusion-doped (Bi-Pb)-2223 superconductor have been investigated. First, iron was evaporated on Bi-2223 superconductor and then the Fe layered superconductor was annealed at 830 °C for 10, 30 and 60 h. Static Vickers hardness, dc electrical resistivity, X-ray diffraction and scanning electron microcopy have been carried out to assess the effects of Fe doping. These measurements indicates that Fe doping, in comparison with the undoped samples, increased the critical transition temperature, and improved formation of high T _c phase, while decreasing the number and size of voids. Moreover, both microhardness and grain size were also enhanced by increasing the amount of diffusion. The values of microhardness were found to be load dependent. In addition, we have investigated the indentation size effect (ISE) behavior using some models such as the Kick’s law, modified proportional specimen resistance (MPRS) model and the Hays- Kendall (HK) approach. Among them, both HK and MPRS models are successful. In this study, the possible reasons of noticed improvement on mechanical and physical properties due to iron diffusion are discussed.     

<Emphasis Type="Italic">p</Emphasis>-AgCoO<Subscript>2</Subscript>/<Emphasis Type="Italic">n</Emphasis>-ZnO heterojunction diode grown by rf magnetron sputtering

P-type transparent semiconducting AgCoO₂ thin films were deposited by rf magnetron sputtering of sintered AgCoO₂ target. The AgCoO₂ films grown by rf sputtering were highly c-axis oriented showing only (001) reflections in the X-ray diffraction pattern unlike in the case of amorphous films grown by pulsed laser deposition (PLD). The bulk powder of AgCoO₂ was synthesized by hydrothermal process. The optical bandgap was estimated as 4·15 eV and has a transmission of about 50% in the visible region. The temperature dependence of conductivity shows a semiconducting behaviour. The positive sign of Seebeck coefficient (+220 μVK⁻¹) indicates p-type conductivity. Transparent p-n heterojunction on glass substrate was fabricated by rf magnetron sputtering of p-AgCoO₂ and n-type ZnO: Al thin films. The structure of the diode was glass/ITO/n-ZnO/p-AgCoO₂. The junction between p-AgCoO₂ and n-ZnO was found to be rectifying.